The invention relates generally to sound absorbers and more specifically it relates to a sound absorber or muffler for intermittently discharged gaseous working medium such as, for instance, compressed air discharged from a pneumatic rotary piston engine. Sound absorbers of this type have a discharge conduit including at least one portion in which the direction of flow of the discharged medium is changed and another portion defining a plurality of consecutively arranged overflow regions each having an alternatively varying cross-section. These known sound absorbers, however, in addition to continuously varying cross-section of one discharge conduit portion, have also abruptly varying overflow passages where irregular reductions and increases of the cross-section of the conduit and sharp deflections of the stream of the gaseous medium about 90.degree. or even more, take place. This non-uniform guiding of the exhaust air contributes to the creation of partially desired vortexes which, however, counteract the sound absorbing effect.
Furthermore, in the known sound absorbers a small portion of the main exhaust air stream is branched through borings that are distributed in a radial and axial plane about a fraction of the wavelength of the vibrating air column in order to generate interference in the exhaust air stream. The small amounts of the branched air, however, can generate the desired interference only on a very limited scale and, therefore, they contribute to the total sound deadening only unsubstantially.